Thin inorganic layers are commonly used to provide barrier properties against moisture in electronic devices, such as for example in opto-electronic devices such as displays and lighting devices. In addition, thin inorganic layers are often used in electronic devices for transparent conductors, for instance ITO (Indium-tin oxide), photovoltaic layer (Si in solar cells), electrical isolation, or dielectric layer in for instance thin film transistors or capacitor structures, or passivation layers on top of an electronic device. The inorganic layers are often manufactured from for example silicon dioxide, silicon nitride or alumina.
For current electronic devices, barrier properties are achieved by arranging the thin inorganic layers in a multi-layer stack, consisting of several inorganic layers, or in a layer stack with alternating inorganic and (organic) polymer layers.
The barrier properties against moisture are limited by the water vapor transmission rate (WVTR). It is determined by intrinsic material permeation of the layers and the number of weak spots, such as pinholes and cracks within the inorganic layers. Hence, the layer stack must show very low concentration of cracks at service, otherwise moisture may diffuse to functional parts and cause reduced performance and failure of the device. This is a complex technical problem, since the inorganic layers used as barriers often are very thin and composed of materials which are brittle, and hence are susceptible for crack-formation resulting in penetration and exposure to moisture, which, in turn, causes decreased performance or failure of the electronic device. Also such brittle layer are often adjacent to relatively soft material layer causing even higher susceptibility for crack-formation.
Also, for other brittle inorganic layers in electronic devices, brittle layer such as transparent conductors, for instance ITO (Indium-tin oxide), photovoltaic layer (Si in solar cells), electrical isolation, or dielectric layer in for instance thin film transistors or capacitor structures or passivation layers on top of an electronic device are very sensitive to crack-formation. Especially, a technical problem is that cracks often form in inorganic layers close to a contact site.
Due to crack formation within in a functional layer the functionality of the layer is lost. For example, a crack in a barrier layer affects the barrier properties strongly, and a crack in a conducting layer might result is a significant change of the electrical performance of the device.
U.S. Pat. No. 7,348,212 shows an example of an electronic device comprising a contact site. The document describes a method for providing a semiconductor light emitting device wherein a light emitting layer is disposed between an n-type region and a p-type region and wherein contacts are electrically connected to the n-type region and the p-type region.
However, there is still a need in the art to improve the performance of brittle inorganic layers in electronic devices, especially for a brittle layer which is to be arranged with a contact site.